This invention relates to an ink jet recording apparatus comprising a recording head moving in a width direction of recording paper for jetting ink drops toward recording paper based on print data, thereby printing an image on the recording paper and a control technique of cleaning of the recording head for sucking ink from nozzle orifices of the recording head of the recording apparatus for recovering the print function of the recording head.
An ink jet recording apparatus, which produces comparatively small noise at the printing time and moreover can form small dots at a high density, is much used for printing including color printing in these days.
Such an ink jet recording apparatus comprises an ink jet recording head for receiving supply of ink from an ink storage section of an ink cartridge mounted on a cartridge, a subtank, etc., and paper feeder for causing recording paper to make a relative move to the recording head. While moving the recording head on the carriage in a width direction of recording paper, the ink jet recording apparatus ejects ink drops to the recording paper for recording.
The recording head capable of jetting black ink and yellow, cyan, and magenta color inks is placed on the carriage and makes it possible to execute not only text printing in black ink, but also full color printing by changing the jet percentage of the inks.
Since ink pressurized in a pressure generating chamber is jetted to recording paper as ink drops from a nozzle for printing, the recording head involves a problem of causing a print failure because of a rise in the ink viscosity and hardening of ink caused by vaporization of a solvent from nozzle orifices, for example, adhesion of dust, mixing of air bubbles, etc.
Thus, if the nozzle orifice is clogged or the ink cartridge is replaced, the nozzle formation face of the recording head is sealed by capping unit and ink is sucked and discharged from the nozzle orifice by negative pressure from a suction pump, whereby clogging caused by ink hardening in the nozzle orifice, etc., and an ink jet failure caused by mixing air bubbles into an ink flow passage are dissolved. This function is called cleaning operation.
To execute the cleaning operation, it is effective to cause a flow as fast as possible to occur in ink in the ink flow passage from the ink storage section to the nozzle orifices of the recording head, for example, whereby the air bubbles existing in the flow passage as well as the ink having increased viscosity can be discharged.
However, to increase the flow velocity of ink at the cleaning operation time, the capability of the suction pump needs to be increased to provide large negative pressure.
To do this, the pump must be upsized and a large-sized motor for driving the pump must also be used; it is inevitable to increase the costs and upsize the whole recording apparatus.
Then, a recording apparatus having the following configuration is proposed. A valve unit that can be opened and closed is placed in the ink flow passage between an ink storage section and a recording head and to perform cleaning operation, when sucking ink is started through capping unit, the valve unit is closed and when negative pressure in the capping unit rises, the valve unit is opened, whereby the flow velocity of ink in the recording head is increased instantaneously.
The described configuration makes it possible to comparatively easily discharge ink hardened or having increased viscosity in the proximity of the nozzle of the recording head without providing a special suction pump for producing large negative pressure.
Since the suction action from the nozzle is performed instantaneously, it is also made possible to produce the cleaning effect in a comparatively small discharge amount of ink as a result.
By the way, the ink cartridge of the ink storage section for supplying ink to the recording head generally has an outer case made of a material of polypropylene, etc., into which a porous substance is loaded for retaining ink. When the ink cartridge is shipped, it is deaerated, whereby the replacement load property (reliability of the operation of the recording apparatus when the ink cartridge is replaced and a new one is loaded) can be provided.
After the deaerated ink cartridge is loaded into the recording apparatus, the atmosphere gradually flows into the ink cartridge through an opening made in the top face of the ink cartridge as ink is consumed. Thus, the deaeration degree of ink in the ink cartridge lowers.
While a sufficient deaeration degree in the ink cartridge is provided, if ink is sucked by the capping unit, air bubbles smaller than the nozzle diameter occurring in the cap flow backward into the head flow passage by negative pressure of the ink cartridge, but disappear because the air bubbles are smaller than the critical radius.
While a sufficient deaeration degree in the ink cartridge is provided, minute air bubbles in the ink flow passage also dissolve in ink; consequently, the probability that a print failure will be caused by dot dropouts caused by air bubbles is low.
However, if the deaeration degree of ink in the ink cartridge lowers, the capability of dissolving minute air bubbles also lowers, so that the effect of air bubbles is received and a problem of a print failure, etc., occurs.
Then, when the cleaning operation of the recording head is performed, negative pressure is applied over a predetermined time, whereby the deaeration degree of ink in the recording head can be raised and the air bubbles produced by the deaeration action from ink grow with other air bubbles in one body, then the air bubbles are pushed out in a stroke by the ink flow.
In a recording apparatus as described above, generally ink cartridges containing black ink and color inks can be attached onto a carriage on which a recording head is placed detachably from above the carriage, and ink is supplied from each ink cartridge to the recording head via a hollow ink supply needle (also called hollow needle) placed upward on the carriage.
In the recording apparatus, the ink flow passage in the recording head is formed very delicately and therefore ink supplied from the ink cartridge to the recording head needs to be in a clean state with no foreign substances of dust, etc., mixed.
That is, if a foreign substance of dust, etc., is mixed, a particularly narrow ink supply port in the ink flow passage of the recording head or a nozzle orifice portion is clogged with the foreign substance, so that the normal ink jetting action cannot be executed and it is made impossible to recover the recording head function in many cases.
Then, generally a filter member for removing foreign substances is placed in the ink flow passage upstream from the recording head, for example, between the hollow needle and a head case supporting the hollow needle, thereby preventing foreign substances from entering the recording head.
FIG. 43 shows the situation in a cross-sectional state. In the figure, numeral 431 denotes a hollow needle on which an ink cartridge 408 is placed for deriving ink stored in the ink cartridge.
The upper end part of the hollow needle 431 is sharpened and an ink derivation hole 431a is made in a part of the upper end part. The hollow needle 431 closely joined to a rubber sealing member 408b attached to the ink cartridge 408 allows ink to derive from the ink cartridge 408 through the ink derivation hole 431a. 
The base end part of the hollow needle 431 is widened to the bottom end and a tapered space 431b is formed in the part.
On the other hand, a space 471a is also formed on the side of a head case 471 of the recording head to which the base end part of the hollow needle 431 is attached, and a filter member 407d is placed between the base end part of the hollow needle 431 sandwiching the spaces.
The spaces are thus provided above and below the filter member 407d with the filter member 407d between, whereby the area of the filter member 407d is made effectively wide for suppressing dynamic pressure (pressure loss) of the filter member 407d. 
As understood from the configuration shown in FIG. 43, in a state in which the ink flow passage formed in the hollow needle 431 and the filter member 407d are placed in a gravity direction, a phenomenon in which an air bubble A remains particularly in the tapered space 431b formed in the hollow needle 431 on the top of the filter member 407d occurs, for example, at the initial loading time of first loading ink into the flow passage of the recording head.
When the ink cartridge is replaced, a phenomenon in which air bubble A enters the space 431b on the top of the filter member 407d and remains in a stuck state in the space 431b also occurs.
On the other hand, if printing is executed with the air bubble A remaining as described above and the printing state is full duty (state in which ink is jetted at the highest frequency at the same time from all nozzle orifices), the air bubble A remaining upstream from the filter member 407d moves slowly to the proximity of the filter member 407d together with the ink flow and remains like flat on the top of the filter member 407d, resulting in a state in balance with the flow velocity of ink.
If the full-duty printing is further continued, a part of the air bubble A passes through the filter member 407d, reaches the ink flow passage in the recording head, and remains therein.
If such a state is entered, the air bubble in the recording head produces so-called cushion action of absorbing pressure change occurring in a pressure chamber based on print data, causing a problem in which it becomes impossible to jet ink from the recording head.
Then, the cleansing operation is executed to exclude the air bubble, as described above. If the valve unit is opened when the negative pressure in the capping unit rises as described above, the flow velocity of ink in the recording head is increased instantaneously, so that the air bubble A is released from the stuck state in the hollow needle 431 and is brought close to the filter member 407d or brought into intimate contact with the filter member 407d, but is not excluded since the negative pressure accumulated in the capping unit also lowers at once; this is a problem.
In this case, a part of the air bubble passes through the filter member 407d and can stay in the ink flow passage in the recording head, also causing a problem in which it becomes impossible to jet ink from the recording head, as described above.
It is therefore the first object of the invention to provide an ink jet recording apparatus and a recording head cleaning control method in the ink jet recording apparatus wherein at the cleaning operation time, a valve unit placed in an ink flow passage between an ink cartridge and nozzle orifices of a recording head is opened for instantaneously increasing the flow velocity of ink and the wait time for promoting the deaeration action is preset, whereby ink having increased viscosity can be discharged and removed and the air bubbles in the ink flow passage can be discharged easily.
It is therefore the second object of the invention to provide an ink jet recording apparatus provided with a cleaning sequence capable of discharging and removing ink having increased viscosity and effectively discharging air bubbles remaining in upper and lower spaces with a filer member between in an ink flow passage and a recording head cleaning control method in the ink jet recording apparatus.